In a hard or floppy disk drive system, a read/write head is moved across the disk so as to be positioned over a selected one of the large number of substantially circular, concentric tracks in which data is recorded and/or reproduced. The head is mounted on a head actuator so as to be positioned at the desired track and the head actuator in turn is driven by an actuator motor. The head actuator, together with other elements in the disk drive system, is mounted on a base plate for clockwise or counter-clockwise motion of the head across the disk.
One operation of the disk drive system is a track access operation or track seek operation in which the head is moved rapidly across a multiple number of tracks from an initial position to a desired track, so as to access the desired track for reading or writing data thereon. It is advantageous that this track access operation be completed as rapidly as possible, since no data recording or reproduction is accomplished during the period of the track access operation. The actuator motor is therefore controlled by a servo control system to achieve an optimum velocity trajectory (velocity-vs-distance) so as to complete the track access operation in the minimum period of time. The optimum trajectory generally requires the application of maximum acceleration to the head in an open-loop operation for an initial period of time until the head velocity and position intersect an optimal deceleration curve, and then the application of deceleration along the optimal deceleration curve for a final period of time to bring the head to rest over the desired track. Obviously, to minimize the initial period of time for the track access operation, the maximum acceleration should be as great as possible under open-loop conditions, and the actuator motor is advantageously a voice coil motor for this purpose. To further minimize the total time, the deceleration is performed under closed-loop conditions and the servo control system is specially tuned by the selection of its components to optimize the deceleration curve. The optimization is improved when a feed forward input is used in the closed loop servo control system.
A special case of the track access operation is the track jump operation in which the head is moved from one track to a closely adjacent track. It is the discovery of the present inventors that, during the track jump operation, the rapid succession of acceleration and deceleration in the specially tuned servo control system causes physical vibrations of the components within the disk drive system. These vibrations are transmitted to the base plate upon which the components, in particular the head actuator, are mounted, causing vibration of the base plate and, hence, low frequency acoustic noise. When a single track jump operation is performed, such acoustic noise, while undesirable, may be tolerated by the operator. However, when a series of track jumps are performed, for example when a disk is being formatted and the head is moved successively from one track to the next across the entire surface of the disk, or in a recalibration operation to find track 0, the regularly occurring acoustic noise becomes decidedly unpleasant. Indeed, depending upon the frequency of the acoustic noise and the structure of the disk drive system, resonance may occur which will not only increase the magnitude of the acoustic noise, but may also affect the physical configuration of the disk drive system and lead to errors in recording and/or reproduction.